1. Field
The invention is in the field of tuning archery bows and archery arrows.
2. State of the Art
For target shooting and hunting, it is important that an archer be able to accurately shoot an arrow from a bow. This means that each time an arrow is aimed and shot from a bow, it should fly similarly to other similar arrows aimed and shot similarly from that bow and hit a target in the same place. In order to accurately shoot an arrow from an archery bow, the bow should be correctly set up and the arrow shaft matched to the bow. The bow set up includes proper adjustment of the tiller of the bow and, for compound bows, timing of the wheels. The bow manufacturer generally provides instructions and information on properly adjusting these characteristics. The arrow rest used should be compatible with either a finger release or a mechanical bowstring release as used by the archer. The arrow shaft should be properly chosen to match the bow's draw length, draw weight, bowstring material, compound wheel type, string release type, and arrowhead weight to be used. Several arrow shaft manufacturers provide selection guides to help the archer select the proper arrow shaft for use in particular circumstances. Further, the fletching, arrowhead, and shaft used have to be matched to provide a correct front of center balance point for the arrow. Generally, the assembled arrow should have a balance point 10% to 15% front of center.
With correct bow set up, arrow shaft selection, and arrow balancing, it is still necessary to properly adjust the positioning of the chosen arrow rest and the nocking point of the arrow on the bowstring in order to achieve repeatable accurate shots from the bow. The nocking point is generally established by a nock locator such as a metal ring or hard or soft yolk on the bowstring. For example, it is common practice to position a metal ring on the bowstring as a positioning guide for the nock of the arrow. The arrow is then always nocked immediately below the ring. These adjustments are generally involved in "tuning the bow". An arrow shot from a bow properly tuned for that arrow will travel accurately as aimed in a substantially straight line with minimal wobbling or porpoising. However, arrows of different weight and/or balance point may not fly accurately as aimed.
There are several methods commonly used in tuning a bow. One is to shoot several similar arrows at a target and make adjustments to the arrow rest and nocking point indicator until the several arrows when similarly aimed and shot by the archer all hit the target relatively close to one another and relatively close to where aimed. Broadheads are not generally used for target shooting and the arrows used here will generally have a field point. Another is to shoot an arrow through a piece of paper and observe the hole made by the arrow as it passes through the paper. Ideally, the hole should be no bigger than the arrow fletching indicating that the arrow passed straight through the paper. An elongate hole indicates the arrow is not aligned in the direction of flight or excessive wobbling or porpoising of the arrow is taking place. It has been suggested that a bare shaft, i.e., without fletching, be used so that the fletching does not rip a large hole in the paper. In this way, the hole formed more accurately shows movement of the arrow. However, removal of the fletching changes the weight and balance point of the arrow so the bow would not be tuned for a normal arrow if tuned to a bare shaft. Arrows used for paper tuning also generally have a field point rather than a broadhead hunting point. A broadhead would make a larger hole in the paper so it would be very difficult to determine the arrow flight characteristics. Tuning by any method using an ordinary field point does not produce a proper tune for an arrow with a broadhead. The balance of the arrow is different in each case. Even if the point is of the same weight as a broadhead to be used, the broadhead changes the balance point of the arrow.
Various devices have been developed to help tune a bow by locating a nocking point on the bowstring, see, for example, U.S. Pat. Nos. 5,175,937 and 4,596,229, and various stands or shooting machines have been developed for drawing and releasing a bow in a set repeatable manner so adjustments can be made to obtain repeatable arrow performance under the same shooting parameters, see, for example, U.S. Pat. Nos. 5,628,300, 5,121,736, and 4,993,397. However, while these devices may provide a rough tune and starting point for a fine tune, they cannot finely tune the bow to the archer's particular shooting style.
The problem of the change of balance of the arrow when changing from a field or target point to a broadhead has been recognized by U.S. Pat. No. 5,496,043 which describes a special broadhead which fits over the outside of the forward portion of the arrow shaft so that the overall length of the arrow remains substantially the same with a field point or with the special broadhead. However, the method disclosed in the U.S. Pat. No. 5,496,043 limits an archer to use of the special broadhead disclosed and does not work for the many varying broadheads currently on the market or currently owned by various archers. Most archers will probably have a number of their preferred broadheads and not want to switch to another broadhead.